Sister-sama no Oose no Mama ni

One day, the demon Clod comes to high school student Sister Kris Ibarakawa. He says that he has a contract with Kris's estranged father to make her happy. He is very serious even for a demon, and says, "I will definitely make you happy," and uses various kinds of magic... Will Kris be able to follow the path of a pure and righteous sister?